The concept of total etch adhesion for enamel and dentin is known. The total etch technique relates to the simultaneous etching of enamel and dentin using a phosphoric acid gel in order to remove a smear layer and to make microporosities accessible for a subsequently applied dental adhesive composition. The acid is completely removed by subsequent air-water jet spray washing. The tubule apertures are sealed by the protective bonding agent layer with resin tags adhering to the tubule walls and the resin-impregnated dentin surface.
However, the total etch technique is problematic in that excessive drying of the etched tooth surface (especially dentin) may lead to inferior bonding properties. In order to avoid a separate etching step and the problems associated with subsequent acid removal and drying, self etching compositions were proposed. Self etching composition typically have an acidic pH of less than 2 and are capable of passing the smear layer. However, the self etching technique gives rise to further problems even when a self cure activator is used for curing. The dental cement is frequently inactivated at the interface to the dental adhesive so that bonding and curing cannot proceed efficiently.
It is the problem of the present invention to provide a dental adhesive composition for use in a total-etch adhesive bonding technique wherein the problems associated with excessive drying are avoided and wherein an improved adhesion in terms of shear bond strength to dentin and enamel is provided at a level of at least 15 MPa, and whereby the adhesion to enamel and the adhesion to dentin in terms of the shear bond strength are of similar magnitude.